Effect of electrolyte composition on the active-to-passive transition behavior of 2205 duplex stainless steel in H₂SO₄/HCl solutions

Selective dissolution could occur in duplex stainless steels (DSSs) due to the difference in chemical composition between the two constituent phases. In this study, the effect of H₂SO₄/HCl composition on the selective dissolution behavior was investigated. The results indicated that there were two distinct peaks appeared in the active-to-passive transition region in the polarization curve. The peak appeared at a lower potential region was associated with the preferential dissolution of ferrite phase while that for austenite at a higher potential. In the concentration ranges of 0.25-2 M of H₂SO₄ and 0.25-2 M of HCl, the magnitude of the peak anodic current density and the resolution between these two peaks greatly depended on the composition of H₂SO₄/HCl. However, the anodic peaks corresponding to the respective dissolutions of ferrite and austenite became less distinguishable when the concentrations of HCl exceeded 1.2 M. Image analysis using scanning electron microscopy (SEM) was performed to confirm the selective dissolution of each constituent phase after potentiostatic polarization at the respective anodic peak potential.